<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style type="text/css">
		/* 权重：未作用在标签上 */
        #box1 #box2 {
			color:red;
		}
        /* 作用在标签上，权重重 */
		div {
			color:blue;
		}
	</style>
</head>
<body>
    <div id="box1" class="div1">
		<div id="box2" class="div2">
			<div id="box3" class="div3">
				<p>我是段落</p>
			</div>
		</div>
	</div>
</body>
</html>